


His Stuttering Heart

by Krystal_Twi



Category: Undertale (Video Game)
Genre: Alternate Universe - Underlust (Undertale), Cussing, Jealousy, Kindred Spirits, M/M, Papyrus mentioned, Rust, Sanscest - Freeform, Underfell Sans (Undertale), Underlust Grillby mentioned, hints to bullying, self hate, sfw, strip bars
Language: English
Status: Completed
Published: 2018-11-24
Updated: 2018-12-03
Packaged: 2019-08-28 13:03:07
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 3,344
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16723935
Author URL: https://archiveofourown.org/users/Krystal_Twi/pseuds/Krystal_Twi
Summary: Red didn't care what people thought or did. Why should he?He also shouldn't care if Hearts, Underlust Sans, didn't flirt with him. Hearts flirted with everyone with that -adorable- stutter of his. Flash a smile, wink and give a flirty comment. He did this to everyone, everyone but Red.





	1. First meeting

**Author's Note:**

> First chapter is how they met. Second will be the actually plot I've promised forever ago.

_Red wasn't the most liked of all the Sanses there was. He knew this and fine with it. Why should he care what the free xp thought of him? He shouldn't. He didn't._

 

_He also shouldn't care if Hearts, Underlust Sans, didn't flirt with him. Hearts flirted with everyone with that - ~~adorable~~ \- stutter of his. Flash a smile, wink and give a flirty comment. He did this to everyone, everyone but Red. _

 

Red could remember when they first meet. Hearts, like Red, wasn't automatically accepted into the group. His revealing clothes and sexual tendencies weirded out most of the others. Red could feel a growing heat in his soul when he saw how quick his friends were to judge the other. It wasn't fair to judge a monster by their au, he should know...

 

Red was first introduced to the other one night in the multi-void. He was getting ready to leave and go home before he got yelled at by Edge when he heard alarmed yelps. Red had rounded the corner to see Underlust Sans pressed into a corner. His eyes blazing in warning but the Sans cornering him was a Sans from a darker universe. UL Sans seemed annoyed at best as he had tried to get away from the monster. Only for the other to grab him and pull him close.

 

Red felt a growl rumble in his throat. Before he knew it, he was standing between UL Sans and the newcomer. His one hand clenching around the monsters, forcing him to let go. The monster growled at him and looked ready to attack for getting in the way of his prey when a Papyrus rushed in and apologized profusely as he tried to get the monster away from Red and UL Sans. Panic in his eyes and he pushed the other away.

 

“ **Keep your Sans in check,”** Red had growled out before pulling UL Sans away from the scene of the Sans know hugging the Papyrus close, looking down right feral in his broken eyelights. The Papyrus nodded his head quickly

 

Red shortcutted the two of them out of there, his hand clasping around UL Sans's. The area around them had snow falling heavily. He could hear the distant sound of loud music coming from Grillbys. They was in Underlust. Red jerked his hand away from Lust. His eyes narrowing at the skeleton beside him.

 

The others eyelights, two large pulsing hearts, shined a brilliant lavender.

 

“Tha-thank you, ” UL Sans said. His lavender heart eyes sparkled with gratitude. It set off something strange in Red. “I don't think an-anyone from the Multi-void has ever st-stood up from me, ”

 

Red cleared his throat and refused to look at the other. A faint blush on his cheeks. Hoping the harsh cold would be good enough excuse for the sudden red in his face. “Don't think anything about it, ” he ground out

 

The smaller skeleton looked away. A frown settling on his skull. “It wa-was a nice gesture, ” before Red could interrupt him, UL Sans looked up, a playful smile replacing the frown. “It would be **hard** t-to not think of it, ”

 

Red froze before shaking his head. A snicker trying to fight its way past Red's mouth. “Good one, betcha been waiting a **long** time to use that one, ” A giggle erupted from UL Sans. His hand coming up and covering his mouth. Red tried to ignore the way UL Sans looked when he laughed and what said laugh did to Red.

 

Red gave a scary looking smile to UL Sans. His sharp teeth glistening in the night. His one gold tooth standing out and emphasizing the sharpness of each tooth by doing so.

 

“See ya later, Hearts, ”

 

“H-hearts?” The underlust skeleton echoed, giggles slowly coming to a stop.. His eyelights brightened as he cocked his head to the side.

 

The smaller one looked generally confused. “I'm usually referred to s-something sexual. Sin, Lust, whore, slut, ” Hearts ranted off the names, counting each on his finger as he went. “Even D-daddy once but never Hearts,”

 

Red held back a scoff, instead, he shrugged his shoulders and looked away. “It fits you, ” Was all he said. Was it hot out here? Or just Red? Fucking hell…

 

Hearts took a step closer being cautious of the edgy skeleton. A pretty lavender blush on his face as his eyes vibrated brighter. His hand going behind his back and punching his other arm as his eyelights searched the other. Red didn't like being under the others gaze like this. It was different. It wasn't cold like Boss's, it wasn't pitiful like Chillby. It was warm and hesitant.

 

“H-how so?” The stutter was still there, but his voice was smooth like butter despite that.

 

A red flush flooding the much larger skeleton's skull. “You're eyelights- Look does it matter!?”  a growl pierced its way from Red's throat. The smaller skeleton didn't flinch, instead, straightened their posture. Their eyes widen in slight shock before softening. A smile filling their face.

 

“No, I g-guess not, ”

 

Red finally looked at the other. He sighed and ran his hand over his skull in frustration. Why was talking to this skeleton so difficult? He was free exp, nothing to feel this way over. He stood there with a small, delicate, frame. Clothes that barely protected him from any oncoming attack and he never experience a reset. He wasn't any threat.

 

So why did he make Red's soul pound with that piercing gaze and smile?

 

Red clenched his eyes shut and flipped his hood over his head. His eyes darting away. He took a step back. “I’m leaving, ” he said quickly as he turned his back on the other. He heard a soft ‘okay’ and the jingle of keys.

 

“Th-thanks once a-again, ” the other called out to Red. Red looked over his shoulder to Hearts. A nice smiling on his face and his soul _(god his soul, how can he stand his soul being on display in front of a monster like Red?)_ were shining brightly under his shirt.

 

“Oh, ” Red turned back around, shifting from leg to leg as he ran his eyes up and down the shorter skeleton. Making sure to avoid his ribs and those eyes of Hearts. “The others will get over it, ” When Hearts flashed him a slightly confused stare, he sighed again. Running a hand across the back of his neck. “Their judgemental view of you, ” Red clarified. “They will get over it, trust me, ”

 


	2. Chapter 2

**Notes for the Chapter:**

> Finally done!!! I can hear the bells! Anyways. i like the originally writing of this better. mostly because i like Lust better than Hearts. Why did i write Hearts? Well this is myown headcanons on Underlust, so might as well throw Hearts into it.
> 
> imma die now, hope you enjoy.

True to Red's word, the others slowly warmed up to Hearts. Especially when they found out the reason behind Hearts sexual nature. How when population in Underlust had got so dangerously low, the king forced all adult monsters to take LT in their souls. Hearts being one of the first to have the LT injection, experienced some side effects. His stutter. 

 

Red didn't think he would really ever interact with Hearts after that night. Why would the other want to be around him? So, imagine his surprise when Hearts approached him at the next meeting. A bright, lazy smile on his face as he greeted Red. Red didn't miss the hesitation in his movement though. He didn't miss the worried look in those heart-shaped eyelights.

 

Red forced his body to relax around Hearts, giving the other an unimpressed stare as the smaller planted himself beside him. Hearts seemed content on sitting next Red in quiet as the others mingled (and stared at the odd pair) around them. Red watched Hearts from the corner of his eyesockets. 

 

_ ‘He'll be gone by tomorrow _ .’ Red truly believed that to be so.

 

However, it wasn't. Hearts continued to greet him and stay by his side throughout the meetups. Hearts at first stayed quiet, seeming pleased with the companionship for the time being. Red was grateful for that. He still couldn't get however Hearts presents. Why did this LOVE free monster want to spend so much time with him? The others normally just talked to him for five minutes before deeming it too much and leaving. (Save for the few exceptions of Comic, Stretch, Slim, and a few of the darker sanses.) 

 

After the first few times, Hearts finally talked. He was leaning back in a chair and watching everyone when he dropped a pun. His eyelights shifting to Red for a quick second to catch his reaction. A smile on his face when he saw the reluctant smirk on Red's face. That had been the beginning of a pun war between the two. 

 

The lustful monster grew on Red. Red began to look forward to the get-togethers, just to see Hearts. Sure, they still had trouble finding topic of interest. Japery and puns seemed to be a good enough start.

 

Once they got past the jokes, they was able to bond over having human traits being implanted in their souls. Not an easy topic for them but it felt nice having someone to talk to about the bullshit of their world. Even if the other would never fully understand. They did understand the motion of having to change their entire nature and watch the world around them change forever. 

 

He could see the knowing look in his brothers and friends eyes. Stretch would elbow him when Hearts came into a room. Comic would shrug his shoulders but the grin on his face was almost mocking. Edge wouldn't say anything, his face seeming stoic but Red could see the slight amusement in his eyelights. 

 

He didn't understand why they did that. Not until he made Hearts laugh, truly laugh. His soul speeds up, his face burning as he watched his friend giggle like a maniac at a joke Red,  **Red** told. A pretty lavender blush splashed across his cheeks, his hand barely covering his mouth. It was more beautiful than the sun when they had first been released. 

 

Red had fallen hard for the pretty skeleton and he was the last to figure it out. 

 

Confessing to Hearts should have been easy. They spent a lot of time together. Especially when they started to meet up in each others aus. However, with Hearts, nothing was as simple. Hearts was a very flirtatious monster. Flirty with any monster that came his way with a grin and wink.

 

Any monster but Red.

 

Red didn't understand it. Not completely anyways. Maybe Hearts only saw him as a friend and didn't want to scare him away. Maybe Red wasn't Hearts’ type, though he flirted with Slim and Razz on multiple occasions. (and on the more adventurous of times, Blood)  

 

Maybe his type was a lot more complicated than that. Red knew from whimsical stories Hearts would tell, that he and Passion (Underlust Grillby) had a sexual relationship. From what red could gather, Passion was tall and had a more dominant nature. Slim was tall while Razz had a dominant nature. Red was short and may have a smart mouth but wasn't known for being dominant.  

 

If Hearts’ would happily flirt with them but not Red, what did that say about Red's chances? Red didn't blame Hearts’ for not being interested. Hearts was smart, punny, adorable, and down right cool. Why would he be interested in someone who was a rude, had a high LV, who was worthle-

 

“y-you’re being quiet. W-whatcha thinking?” Red blinked. Hearts sat across from him. His eyelights twinkling in curiosity. The apparently permanent blush on his face shining brightly in the darkness of the noisy club. His fingers slowly tracing the top of his empty glass. Leaning into his other hand. 

 

They was currently at the strip club in Underlust. Hearts was invited by his worlds Alphys, but he had been ditched when Lust!Undyne gave her a booty called. Or so Hearts’ assumed. Hearts called Red beforehand, saying he had a feeling his Alphys would ditch and he didn't want to be alone. 

 

Red found it weird at first, but didn't think anything of it. Underlust was a strange world. Red flashed Hearts a toothy grin, raising an eyebrow bone at him. His previous self hate thoughts gone as Hearts smiled at him. 

 

“Nothin’, just that yer universe has shit music, ” Hearts snorted, his nose crinkling adorably as his shoulders shook. . “What the hell you thinkin’?” Red asked, Hearts looked at him and shrugged his shoulders. He leaned back and looked around the club. His eyes landing on the bar. A smile crawling onto his face. Red followed his gaze, frowning when he saw Hearts looking at coal breath. 

 

“T-that I need a dr-drink, ” Hearts said as he stood from the table. His hand grazing against Red's shoulder as he made his way to the bar. 

 

Hearts plopped himself at the bar. His hand running his fingers carefully up and down Passion's forearm. His pretty heart eyelights sparkling up at the bartender. Red held back the growl that had threatened to escape his mouth. 

 

He raised his quickly empting glass. The mixture of mustard and vodka running down his nonexistent throat. His eyes never leaving the two at the bar.

 

Red's eyelights focused in on the other. Hearts was trying to say something but his face scrunched up in concentration as he tried to get the words out without stuttering so much. Red had seen that expression up close before. Hearts’ stutter becoming more noticeable with each syllable. It was honestly adorable, not that Red will admit that in a million resets. There was a hint of annoyance flickering in his eyelights. Passion snickered at the attempt, leaning in closer to Hearts. His eyes only paying attention to the adorably sexy skeleton in front of him. 

 

Passion leaned his body down, his face inches from Hearts’. He had mumbled something low against Hearts’ skull, only for the other to hear. His flame crackling with untold promises. Hearts’ skull lit up, his entire skull now lavender as he eyelights darted to Red before locking with Passion. A smile playing on the edge of Hearts’ mouth. He winked to Passion, whispering to the barista. 

 

An ugly feeling gripped his soul and twisted it. Squeezing his soul painfully right as he watched the two talk dirty to each other. Red wanted to dust this mother fucker. Who did he think he was? Did he really think he was worthy of Hearts? Hell nah. Red wasn't good enough either but at least he could protect him and actually love him and not use as a toy! 

 

The glass in his hand shattered.

 

Shards of glass impaled into Red's hand. He didn't flinch, he felt worse. His eyes never leaving the two at the bar. Passion had looked up however. His sudden lack of personal attention had caused Hearts to turn his own head. His heart eyes shrinking in shock as he jumped off the bar stool, leaving his mayo and wine (Red will never understand his taste) mixture. His body moving easily among the crowd to get to Red 

 

Hearts hands hovered over Red's hand. Unsure what to do. “R-red! What ha-happened?” 

 

Red slowly broke the one sided glare war with the tiki torch and looked to his hand. The pieces wasn’t small and the shards that was in his bone wasn't in deep at all. An easy fix for Red, he has had worse from his bro on a  **good** day.  

 

Hearts seemed to decide on what to do, his hands lowering and carefully trying to pull the glass out. Red resisted the growl as he pulled (yanked) his hand away. Bitter jealousy still biting at his soul and clouding his judgment along with the wince of pain. 

 

“I'm fine, ” Red roughly, but quickly, pulled the shards from his bone. Marrow trickling from the cuts. He heard Hearts gasp out a ‘wait!’. His own hands glowing with healing magic as he tried to stop Red. 

 

His magic healed the wounds but didn't stop Red from getting the glass out. It would scar but scars was good in underfell. He could spread a lie about his he strangled some skeleton monster and bone fragments embedded in his hand. Better than saying he got jealous over a bartender flirting with his friend. 

 

Hearts sighed. “Red, what happened?” He asked again, this time his voice steady enough to not stutter. His eyelights hardened and calculating Red's every move. No matter how much LUST Hearts had in his soul, he was still a Sans. 

 

“What'z it to ya?” Red hissed out. Hearts frowned. Directing his anger at Hearts wasn't right, but seeing Hearts act caringly towards him after flirting with Passion stirred something ugly in him. 

 

“R-red, I-” 

 

Red cut him off, shoving himself away from the table harshly. “Save it, let's just get outa here, ” Red pushed passed Hearts, shoving his hands into his jacket pockets and kept his gaze away from the hurt eyelights of the monster that plagued his thoughts. 

 

His shoved past all the monsters in the strip club. Not slowing down, even as Hearts called for him. He could hear annoyed mumbles from the monsters he pushed past. He didn't care for them though. He could see the exit in sight. Once he was out of this damn place he was teleporting home and breaking a few things. 

 

A hand grabbed a hold of his arm when sudden darkness and coldness enveloped him. Static raging through his ears for a split second before light blinded him and he was turned around roughly, looking down at bright, concerned, heart shaped, eyelights. 

 

They was in front of Hearts house. 

 

“What i-is wrong, Red?” Hearts all but growled. His hand letting go of Red's arm, letting him have a chance to run. “D-did something happen wh-when I was ta-talking with Passion?” 

 

Anger flared in Red’s soul at the mention of that rat bastard. He held back a growl and glared just above Hearts’ head. “It d-did, didn't it! Did so-someone make a pass at you?” 

 

If Red payed attention to Heart's, he would have heard the annoyance and anger that sounded in Hearts’ voice. Not liking the idea of someone hitting in Red when he wasn't around.  What Red did do was snort and roll his eyes. 

 

“R-red!” He finally looked down at Hearts. He could see the other Sans’ frustration, his muscles tensed, hands clenched at his sides as he stared at Red. Red felt slightly guilty at being the reason the normally relaxed skeleton looked off hinged. “Tell m-me what’s wrong!” 

 

Red licked his mouth, sighing and wiggling his fingers. “Why…” Red swore under his breath. He wanted to puff out his chest and tell a random pun, to ease Hearts’ concern. He also knew Hearts was too smart for that. 

 

“Why don’t you flirt with me?” Red finally got out. Hearts frowned and tilted his head to the side. 

  
“W-what?” Hearts asked confused. 

 

“You flirt with everyone else  **but** me,” Red exclaimed running his hands across his skull. “What is it? Am i repulsive?”    
  
“No, of c-course not.” Hearts reassured. 

 

“Then am i ugly or something?” Red asked. Hearts quickly shook his head. 

 

“No!” Hearts exclaimed, seeming shocked at the very idea. He raised his hands and stepped closer to Red.

 

“Then what is i-” Red was cut off when he soon found Hearts’ mouth on him. Hearts’ hands was clinging to his face and holding him close. His eyes was squeezed shut and his nose was scrunching up in that adorable way.

 

Red closed his eyes and kissed him back. Red wrapped his arms around Hearts’ waist, pulling him close. Hearts’ hands wrapped loosely around Red’s neck, sighing into the kiss. Hearts pulled back but didn't go far. He kept leaning forward and kissing Red repeatedly. 

 

Hearts pulled back, but didn't go to far. “Y-you  _ really  _ don’t know anything a-about Underlust monsters.” Hearts whispered against Red’s mouth. His breathing uneven and his eyelights turned to bright hearts. His eyelights sparkling in amusement, Red shook his head.

 

Red tightened his hold on the monster in his arms. “Not a damn thing.” Red whispered back before kissing Hearts again. 

  
  
  
  
  
  


**Notes for the Chapter:**

> using a bluetooth keyboard and accidently went back when I was about to post....had to redo everything all over again XD. brings flashbacks to when I kept deleting a comment i was tryin to post when I first got on ao3
> 
> Anyways. Story details
> 
> Hearts was going to confess his feelings to Red that night anyways, but was really nervous so he went to talk to Passion. 
> 
> In this Underlust characters flirt with everyone BUT the person they are romantically into. It is their way of showing they see and feel differently for that person. If they flirted with everyone, it would be hard to tell if they actually liked you or was just treating you like everyone else.
> 
> Hearts may have set up the whole thing to make sure his Alphys bailed on him. He just wanted an excuse to have some one on one time with Red. 
> 
> let me know if you see any mistakes! I hope you enjoyed! leave a comment and have a great day

**Author's Note:**

> Headcanon: Hearts has a stutter due to being one of the first to get the LUST injections and the dosage was extremely experimental in that stage. 
> 
> Lust was never attacked like he was in the chapter before. When he talks Bout people not standing up for him, he means rude comments and so on. Red is one of the first to actually do something about it. 
> 
> Res was also shunned by the others at first and since I headcanon that Red did have sex for survival when he was younger, he definitely doesnt like Hearts being shunned either. 
> 
>  
> 
> Also kind of dedication this chap to three people from tumblr for their kind words on a post of mine.  
> Papayapaperss  
> Alinmenttreasure  
> And Random-Genie  
> Thanks you three so much.
> 
> Please, if you liked, leave a comment, it gives me inspiration to write more :3


End file.
